op wilmington



Patented Aug. 1929. I.

' UNITEDISTATES 1,725,.564 PATENT" OFFICE.

WILLIAM s. cALcorr AND wamm A. DoUeLAss, or PENNS enovE, NEW JERSEY, AND OLIVER M. HAYDEN, F wrnmmeron, DELAwAaE, 'Assrenons 'ro E. 1. 'no PONT DE NEMOURS a COMPANY, or wrmrme'ron, DELAWARE, A conronArron OI DELAWARE.

PROCESS or nErAEDIne DErEEIonArIoN or nuD'EEn AND :enoDUcr. a

No Drawing.

This invention relates the art of retarding the deterioration of rubber or rubber-containing materials by the incorporain retarding deterioration. More particularly the invention involves'the use of certain combinations of chemicalxsubstances which jointly retard the deteriorations caused by heat and oxygen.

1 The deterioration of rubber. goods has been thought to be due largely to oxidation of the rubber compound. This deterioration is very slow at ordinary temperatures and therefore to make possible the comparison of the aging 1 5 characteristics of various mixes. for the pro duction of rubber goods, accelerated aging,

tests have been developed. The older of these tests commonly known as the Geer oven test consists in subjecting samples of vulcanized rubber to a slow stream of airat a temperature of 70 C. Due to the fact that in use certain compounds such as inner tubes of bus tires, are occasionally subjected to tem:

peratures as high. as 90-"-'100 0;, the Geer oven temperature has been raised by some investigators to these higher temperatures.

It was found that certain stocks aged in the Geenoven did not give the same results asby natural-aging and with the belief that 33 this difference "was due to' an over-emphasis of the thermal efiect, the oxygen bomb aging test was developed. In this test the effect of oxygen is increased by carrying out the accelerated aging test'under 300 lbs. oxygen pressure at a temperature of or (l1 Under these conditlons the accelerated aging test gave the same type of deterioration as i that obtained b'ynatural aging.

We have found that a reagent may be very "g -eflicient as an oxidatio'n inhibitor as u-shown by the oxygen bomb test, and without ciable effect as a heat' -resister, 'whext f in the Geer' oven. On theother hand, other v g compounds may be much more efficient as heat res1sters' and much less eflicient as oxidation inhibitors. Although it is probable that the effects of heat-and o'xy en are not entirely independent of each ot er, no onereagenttion. tion of certain agents having specific eflfects mercial antioxidant.

Application filed Rovember 19, 1927. Serial lI'c. 234,549

tested has been found to be equally eflicient in preventing these two types of deteriora 6 The primarypbject of our invention is to retard the detenoration of rubber caused by .heat and. oxygen by the incorporatidn, of a combination of reagents, the vcomponents ig-.5

. the combination being specifically adapted t6 the prevention ofa certain type of deterioration.

Another-object is to retard the deterioration ot rubber by the use of a ,mixture of pure 60 materials, easily duplicated and standard- .ized.-; Other-objects will appear hereinafter.

We have. discovered that certain secondary aromat1c ammes, such as phenyl-a'lpha-n'ap'h-'- .thylamine, are outstanding as oxidationin c5 bomb for forty-four days at 703.6. under 300 lbs. oxygen pressure. A lcontrol sample cured tothe same degree was completely deterioratedjin three days, whileanothercontrol sample containing the optimum amount of a commercial antioxidant had deterio -rated completely in fourteen days. When the same stock was subjected to an accelerated aging test in the Geer oven at 70 or 90 6., 30

the resistance to deterioration, althoughbe't- I ter than the control,.-containing no antioxidant,- was inferior to the-resistance obtained by the use of the optimum amount ofv a com- I Aromatic diamino compounds, such as meta toluylene diamine, although difficlllt-tOfdiS perse satisfactorily, have been shown'to os- ".sess exceptional heat-resistingqualities w en testedin the Geer oven at 70 "or. 90810., but 90 onlyfiroderate resistance to, deteriorati when subjected to an accelerated-agingltest in the oxygen bomb? 3 j With the appreciation of the specifie as.

tion 'of certain .age-resisting mater'1ials, we'os have discovered that amixture i'mproved age-resisting properties is obtained by combining two or more materials, each of which contributes its specific property. Since these mixtures are composed of commercially pure compounds, easily analyzed and standardized, the resulting mixtures are of uniform composition and can be duplicated.-

As a specific example, 100 parts meta. toluylene diamine, 100 parts stcaric acid, and 200 parts phenyl-alpha-naphthyl'amine are melted together and subsequently converted to the solid form by any of the well known methods which will give a uniform product. This mixture has been found to impartexceptional resistance to deterioration to various typical stocks tested in both the oxygen bomb and the Greer oven.

- Other secondary aromatic amines and arolene diamino, or B-B-di-naphthylamine and in place of meta-toluylene diamine we may substitute meta-phenyleue diamine.

By way of further exan'iples we have discovered that non-accelerating aldehydeamine condensation products such as the acetaldehydeaniline acid condensate and aromatic diamino compounds such as metaphenylene-diamine, meta-toluylene-diamine, henzidine, tolidine, dianisidine, naphthalene diamino. etc, are eflicient in retarding the type of deterioration which takes place in the so-called Greer oven at 90 C. This class of substances may be termed heat resisters or agents, primarily retarding deterioration due principally to heat. "When l e compounds are incnrporated into a rubber mix, and the vuicanized rubber is subjected to the oxygen bomb test at C. under 300 lbs. oxygen pressure, it is found that although there is some retardation of the deterioration,'they are not as effective as certain other compounds hereindescribed which are particularly effective in retarding deterioration due pri marily to oxygen.

As further examples of such oxygen resisters, that is to say, compounds whose primary function is to resist deter oration due to oxygen, we have found the following: thiourea, certain compounds containing the imino group, diphenyl-amine, the various ditolyl-, xylol and mixed phenyl, tolyl or xylyl-amines, phenyl beta naphthylamme, the tolyl, xylyl and dinaphthylamines, and diphenyl ethylene diamine, etc. When' these compounds are used in rubber mixes which are tested in the Geer oven, it is found that there is some retardation of the deterioration, but not somuch as that imparted by the aforesaid heat resisters.

Compounds which have been found to exhibit a specialized heat resisting or oxidation resisting function are grouped below:

Group A. I (Compounds whose primary nclion retards the deterioration due to heat.)

Essentially non-acreiernt- 1.

mg aeclaldehyde amine Group B. (Compounds whose primary action retards the deterioration due .to oxidation.) Diphenyl ethylene (ii amine.

condensation products. 2. Diphonylnmiuv. 2. Meta phenylenc diamino. 3. Various diotoiyl amines: 3. Meta loluylone dialnine. -py "mine 4. inrnzidinv. lJi-m-tolyl amine 5. Dinnisidim'. Di'o-rolyi amine. 6. Tolidinu. Mixed tolyi amines: 7. Naphthalene dinmliit'S. -1 m ne o-in tolyl amine p-m toiyl amine. Phcnyi tolyl amines.

. Various dixylyl amines.

. Mixed phenyl-tolyl, xylyl naphthylamines, phenyi -a nuphthyiumiue, tolyi-a-naphtbylumlne. phv uyi-betu-naphthyl- :UUlill.

7. Diiuiphthylainines:

a-a-dinaphthylamine b-hdinuphthylamine.

8. Mixed naphthylamiues:

u-h-naphthyiaminea.

Gist-vb There'is also an intermediate class of substances which possess neither outstanding heat resisting nor oxygen-resisting properties. As examples, thevarious polyhvdrir. phenols, amino and substituted amino phe nols, aldehyde amine condensation products such as those resulting from acetaldol and alpha naphthylamine, are given.

Still further illustrations of the principles of this invention consist in -the following procedures:

Mctieod of producing a rubber composition which possesses exceptional resistance to dczm'zm'atzon when tested in the oxygen bomb.

A homogeneous mixture of 10 parts B B dinaphthylamine and 1 part meta phenylenediamine is made by any of the well known methods and L25 parts of this mixture are incorporated into parts rubber, 18.15 parts zinc oxide, 2.25 parts sulfur and 0.625 parts di-ortho-tolyl guanidine. The stock after curing for 45 minutes at 141.5 C. possesses'exceptional resistance to deterioration when tested in the oxygen bomb (oxidation resistance) at 70 C. under 300 lbs. oxygen pressure, but only fair resistance when tested in the Greer oven (heat resistance).

Method of producing a rubber compositz'oa III) ethod of alteiing the age resistant proper- I the amount depending upon the improvement in resistance desired. Conversely, if it is de sired to improve the resistance to' deterloratlon 1n Geer oven, homogeneous mixtures of para-amino-phenol containing dianisidine' may be employed.

Method of producing a rubber composition which possesses exceptional resistance to both types of deterioration. A homogeneous mixture of 100 parts meta toluylene diamine, 100 parts stearic acid, and

200' parts phenyl alpha naphthylamine is melted together and subsequently converted to the solid form by any of the well known methods which will give a uniform product.

By the incorporation of 1 -5 parts of this mixture into a rubber composition containing rubber 100, zinc oxide 18.15, sulfur 2.7 5,- diortho-tolyl-guanidine .5625, a vulcanized rubber is produced after curing for minutes at 141.5 C. which possesses the desired resistance to deterioration when tested in both or either the Geer-oven and the Bierer oxygen bomb. j

The particular mode of introducing the deterioration retarders of this invention may vary according to circumstances, and may occur prior to vulcanization in compounding operations, and also subsequent to vulcanization in other types Off-OPGIfitlOIIS. The said oxidation and heat resistors may be mixed before use, or they may be added in'succession in the process-of manufacture. The particular proportions in'which these oxidation and heat resistrs are respectively used may be varied, but wehav'e'found it highly advantageous to'empl'oy'them in certain definite proportions, therespective amounts thereof eing proportioned directly in accordance with the respective deteriorating effects of oxidation and heat in the exposure to which the rubber article is to be subjected while in use. Thus, if rubber is being manufactured into an article which must in actual use resist deterioration from heat and oxygen equally well, being severely subjected to both influences, it may be found advantageous to use equal proportions of the two inhibitors.

On the other hand, if rubber is to be manu-' fliictured into an article where the-influence of heat in actual use is probably going to'be relatively very small, then the proportion; of

the heat resister will be also relatively much smaller than the proportion of oxidation resister added. An of heat is probably going to be relatively great, then the proportion of heat resister must be relatively increased. Thus, we have found that the resistance to the two types of agent can be independently controlled and vice versa, where the effect at 70 C. and 300 lbs. pressure, and with this information to select pairs of agents which .will jointly resist the effects of oxy en and heat in accordance with the use to w 1ich the ultimate rubber article is to be put. For ex-' oods must resist o-x'ida ample, mechanical tion, but are very se dom subjected to an elevated temperature. In these cases, where a pair of resistors is employed,,the one-would be. in largest proportion which primarily resisted oxidation as shown by the aforesaid testing methods. Again, where gaskets for steam lines are to be manufactured, a resistor would be selected whose primary function is to resist the action of heat. In the case of the manufacture of inner tubes, such-as bus tires, which are subjected to the combined influence of heat and oxygen, approximately an equal proportion of a heat resistor and an oxygen resister would be employed.

It is to be understood that wherever in the appended used it is to include not only natural rubber such as Hevea, balata, or gutta percha but also rubber-like materials made by synthesis and generally known as synthetic rubber, wherever they are subject to deterioration of the character described.

As many apparently widely different emclaims the expression rubber is bodiments of this invention may be made the deteriorating influence of heat,,'and an-.

other which contributes its primary action in retarding the deteriorating influence of oxygen,

2. A- process of retarding the deterioration of rubber under the action'of oxidation and heat, which comprises incorporating into the rubber two 'or more substances, one of which contributes its primary action in retarding the deteriorating influence of heat, and another which contributes its primary action in retarding the deteriorating influence of oxygen, the respective amounts of said substances being proportioned'directly in accordance with the respective deteriorating effects of oxidation and heat in the exposure to which the rubber article is to be subjected while in use.

3. The invention of claim 1, in which the oxidation retarder is a secondary diaromatic amine.

4. The invention of claim 1, in which the heat retarder is an aromatic diamino compound.

5. The invention ofclaim 1, in which the substances are phenyl-alpha-naphthylamine and meta-toluylene-diamine.

6. Rubber containing one component which contributes its primary action in retarding deterioration due to heat, and another component which contributes its primary action in retarding deterioration due to oxidation.

7. A mixture of agents ada ted to retard the deterioration of rubber, sai mixture com-- prising one compound which contributes its primary action in retarding deterioration due to heat, and another compound which contributes its primary action in retarding deterioration due to oxygen.

8. The invention of claim 1 in which a mixture of phenyl-alpha-naphthylamine, stearic acid, and meta-toluylene diamine is added to the rubber.

' ration of rubber, comprising phenyl-alphanaphthylamine, metal-toluylene diamlne, and stearic acid.

.12. The process of retarding the deteriora-' tion of rubber under the action of oxidation and heat, which comprises incorporating into the rubber two substances, each of which is initself effective in retarding the deterioration of rubber the two substances differing in that iftwo rubber com ositions be made, one containing the one so stance and the other the other substance, and these two compositions be exposed to air at 7 0 temperature and atmospheric pressure, one compound will prove more eflective in retarding deterioration than the other, while if the same two rubber compositions be exposed to oxygen at a temperature of and a pressure of 300 lbs the order of effectiveness of the two stances will be reversed.

13. A product for retarding the deterioration of rubber under the action of oxidation suband heat, which product comprises two substances, each of which is in itself effective in retarding the deterioration of rubber, the two substances differing in that if two rubber compositions be made, one containing the one substance and the other the other substance, and these two compositions be exposed to air at 7 0 temperature and atmospheric pressure, one compound will prove more effective in retarding deterioration than t-he'other, while if the same two rubber compositions be exposed to oxygen at a temperature of 7 0 and a pressure of 300 lbs. the order of effectiveness of the two substances will be reversed.

14. A mixture of agents adapted to retard .the deterioration of rubber, said mixture comprising at least one of the compounds of Group A .in combination with at least one of the compounds of Group B.

15. The process of retarding the deterioraone of the compounds ct if-Z-roup A, ogre-err with at least one of the comporn... Group 18. A lllbiJiE' c mpound containing two substances, each of which is in itself eii'ective in retarding the deterioration of rubber, the two substances differing in that if two rubber compositions be made, one containing the one substance and the other the other substance, and these two compositions be exposed to air at 70 temperature and atmosw pheric pressure, one compound will prove more effective in retarding deterioration than the other, while if the same two rubber compositions be exposed to oxygen at a tempera ture of 7 0 and a pressure of 300 lbs. the order of effectiveness of the two substances will be reversed.

'19. A rubber compound containing meta toluylene diamino andphenyl-alpha-naphthylamine.

20. A rubber compound containing a secondary diaromatic amine and a primary aromatic diamino compound.

21. A mixture of agents adapted to retard the deterioration of rubber, said mixture comprising a phenyl-naphthylamine and a primary aromatic diamino compound.

22.; A'mixture'of agentsadapted to retard prising a. primary aromatic diamine and g, naphthylamine and. phenyl-beta-naphthjl- A compound of the class consisting of phenyL lamme. alpha-naphthylamine and phenyl-beta-napb In testimonywhereof we aifix our signathylamine. v tures.

5 24. A mixture of agents adapted to retard r thedeterioration of rubber, said mixture com- WILLIAM S. CALCOTT. prising meta-toluylene-diamine and a. com- WILLIAM A. DOUGLASS.

pound of the class consisting of phenyl-alpha- OLIVER M. HAYDEN. I 

